1. Field of the Invention
The present invention relates to the treatment of hazardous waste and, in particular, to the use of a processing fluid additive for safely and effectively treating water-wet hogout propellant as well as any other water-wet propellants, explosives and hazardous wastes to make them compatible with the MSO (Molten Salt Oxidation) process.
2. Description of the Background
The dynamics of a smelt-water explosion may not be completely understood, but it has long been recognized that it is an event to be avoided. A black smelt explosion is caused by unevaporated water reacting with unburned residue or hot ash at the bottom of the boiler, says Esa Vakkilainen, senior research manager at recovery boiler specialist Andridz-Ahlasperon. For example, a black smelt boiler “explosion” closed Sodra Cell's Norwegian kraft pulp mill at Tofte in September 2000. This resulted in around 80,000 tons of softwood and eucalyptus pulp being lost from market production, affecting both suppliers and customers.
There have been efforts to prevent smelt explosions in kraft mills as above. This is reflected in U.S. Pat. Nos. 3,447,895 to Nelson et al., 4,106,978 to Nelson, 4,194,124 to Nutley et al., and 4,462,319 to Larsen. These patents suggest solutions in the form of (1) introduction of a liquid to rapidly cool the smelt bed (e.g. Nelson et al.), (2) introduction of a water-absorbing powder (e.g. Nelson, Larsen), and (3) irradiation of the smelt/water interface to create non-explosive nucleate boiling (e.g Nutley et al.).
As a result of the foregoing efforts, it is known that polyglycols (polyethylene glycol and polypropylene glycol) can help to prevent smelt-water explosions in kraft chemical recovery furnaces. The ability of polyethylene glycol or “PEG” to prevent smelt-water explosions is described in U.S. Pat. No. 3,447,895 Nelson et al. The '895 patent discloses a method of preventing explosions in kraft chemical recovery furnaces due to water leaking into the molten smelt in the furnace. An aqueous quenching solution of polymeric glycol (polyethylene glycol and polypropylene glycol) is introduced into the furnace to rapidly cool the smelt to safe temperatures without itself causing an explosion.
The risk of smelt explosion also arises in the context of MSO waste treatment. The Molten Salt Oxidation (MSO) process is a thermal, flameless process that has the inherent capability of completely destroying organic constituents of mixed wastes (chlorinated solvents, spent ion exchange resin), hazardous wastes (PCB-contaminated oils), and energetic materials. The MSO process is commonly used for treatment of water-wet propellant and explosive wastes that are typically generated when a propellant or an explosive is removed from its casing using a high pressure water jet. One example of this is hogout propellant. However, smelt-water explosions are also able to occur in high-temperature furnaces/reactor vessels during MSO waste treatment.
Thus, the ability of the polymeric glycols in preventing explosions in kraft chemical recovery furnaces would seemingly make them useful for the MSO process. However, the MSO process is quite different from that of a kraft chemical recovery furnace in that it is a chemical reaction process. The reactants, including solid, gas or liquid wastes concurrently with air, are introduced into a reaction medium, which is molten sodium carbonate or a blend of other salts at temperatures ranging from 700-1000 degrees Centigrade. The reaction medium may or may not enter the reaction, however, it serves as a host to generate combustion products and to facilitate or to catalyze the reaction between the oxygen in the incoming air and the combustion products. Therefore, the MSO process imposes a different set of requirements upon the reactants or feed streams than does a kraft chemical recovery furnace.
Consequently, it would be greatly advantageous to reduce/eliminate the potential for smelt-water explosions that are able to occur in high-temperature furnaces/reactor vessels during MSO by a process that employs polymeric glycol to prevent a smelt-water explosion due to the accumulation of dangerous levels of sodium chloride and/or sodium sulfide in the molten sodium carbonate in the MSO reactor vessel. Sodium chloride and sodium sulfide are known to create a highly explosive smelt in kraft chemical recovery furnaces.